This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A176597 #41 Apr 23 2024 07:16:50
%S A176597 22,33,55,77,1111,1313,1717,1919,2323,2929,3131,3737,4141,4343,4747,
%T A176597 5353,5959,6161,6767,7171,7373,7979,8383,8989,9797,101101,103103,
%U A176597 107107,109109,113113,127127,131131,137137,139139,149149,151151,157157,163163
%N A176597 Double primes: concatenation of the n-th prime with itself.
%H A176597 Vincenzo Librandi, <a href="/A176597/b176597.txt">Table of n, a(n) for n = 1..1000</a>
%e A176597 Concatenation 2 and 2 is 22; 3 and 3 is 33; 5 and 5 is 55; etc.
%t A176597 dp[n_] := Module[{idn = IntegerDigits[n]}, FromDigits[Join[idn, idn]]]; dp /@ Prime[Range[40]] (* _Harvey P. Dale_, Jun 02 2011 *)
%o A176597 (Magma) [Seqint(Intseq(p) cat Intseq(p)): p in PrimesUpTo(200)]; // _Vincenzo Librandi_, Mar 14 2013
%o A176597 (PARI) a(n) = { my(p=Str(prime(n))); eval(concat(p,p)); } /* _Joerg Arndt_, Mar 14 2013 */
%Y A176597 Cf. A000040, A020338, A067087.
%K A176597 nonn,base
%O A176597 1,1
%A A176597 _Vincenzo Librandi_, Apr 21 2010
%E A176597 Edited by _Charles R Greathouse IV_ and _R. J. Mathar_, Apr 23 2010